The digital world has rewired teen brains and made them less able to recognize and share feelings of happiness, sadness or anger, said the UCLA professor of psychiatry and aging, who has also studied adolescent brains.

Small noted that up to 60 percent of synapses in the brain are pruned away between birth and adolescence if they aren’t used. He cited the oft-quoted Kaiser Family Foundation study from 2010 that showed teens spend half their waking hours with technology, from cell phones to computers and/or television. The study found that typical eight to 18-year-olds devote an average of seven hours and 38 minutes to using entertainment media across a typical day, or more than 53 hours a week. Thanks to multitasking, they are actually packing a total of 10 hours and 45 minutes’ worth of media content into those seven and a half hours.

Other researchers disagreed. Teens are adding media interaction to face-to-face interaction, said Amanda Lenhart, a senior research specialist who directs the Pew Internet & American Life Project’s research on teens, children and families. Teenagers say they’d rather be with their friends in person than communicate via electronic devices, Lenhart said.